let MetadataProp = {
	type
		| [| 'derived, 'docinfo, 'docmeta |]
		| doc "Where will we be looking for this metadata?"
		| default
		= 'docinfo,
	title
		| String
		| std.string.NonEmpty
		| doc "Definition title in the document (replaces existing; can be HTML)",
	modifier
		| String
		| std.string.NonEmpty
		| doc "Modifier for the CSS selector (camel case preferred)",
	itemprop
		| String
		| std.string.NonEmpty
		| optional
		| doc "BlogPosting schema prop (see: https://schema.org/BlogPosting)",
	separator
		| String
		| std.string.NonEmpty
		| doc "Separator for multiple values"
		| optional,
	special
		| [| 'date, 'peer, 'keywords, 'license |]
		| optional
		| doc "Special type handling",
}
in
let ValidMetadataField =
	std.contract.from_predicate (fun mps =>
		std.is_record mps
		&& std.record.fields mps
		|> std.array.all (fun field => std.string.is_match "^[a-z][a-z0-9_-]*$" field)
	)
in
{
	author = {
		title = "Writer",
		modifier = "writer",
		itemprop = "author",
		special = 'peer,
	},
	authors = {
		title = "Writers",
		modifier = "writer",
		itemprop = "author",
		special = 'peer,
	},
	contributors = {
		title = "Contributors",
		modifier = "contributor",
		itemprop = "contributor",
		special = 'peer,
	},
	editor = {
		title = "Editor",
		modifier = "editor",
		itemprop = "editor",
		special = 'peer,
	},
	translator = {
		title = "Translator",
		modifier = "translator",
		itemprop = "translator",
		special = 'peer,
	},
	version = {
		title = "Version",
		modifier = "version",
		itemprop = "version",
	},
	date_created = {
		title = "Created",
		modifier = "dateCreated",
		itemprop = "dateCreated",
		special = 'date,
	},
	date = {
		title = "Published",
		modifier = "datePublished",
		itemprop = "datePublished",
		special = 'date,
	},
	date_amended = {
		title = "Amended",
		modifier = "dateAmended",
		itemprop = "datePublished",
		special = 'date,
	},
	location = {
		title = "Location",
		modifier = "locationWritten",
		itemprop = "locationCreated",
	},
	license = {
		title = "License",
		modifier = "license",
		itemprop = "license",
		special = 'license,
	},
	word_count = {
		type = 'derived,
		title = "Words",
		modifier = "words",
		itemprop = "wordCount",
	},
	time_burden = {
		type = 'derived,
		title = "Time burden",
		modifier = "timeBurden",
		itemprop = "timeRequired",
	},
}
	| { _ : MetadataProp }
	| ValidMetadataField
#| doc "Mapping props to key is the Docutils CSS selector (which will be all lowercased & elimates Unicode) for the purpose of shaping the metadata"